Currently, insulation impedance of non-isolated photovoltaic grid-connected inverters is prescribed in photovoltaic grid-connected standards in many countries, such as VDE-0126, UL1741, etc. It requires that insulation impedance of the photovoltaic array which connected to the grid connected inverter is not smaller than a specified value before starting grid-connected operation. Therefore, in corresponding non-isolated grid-connected inverter products, insulation impedance of the photovoltaic inverter needs to be detected before conducting the grid-connected generation operation.
Currently, in the market, demand for multi-inputs of inverter products is growing. However, existing detection methods for detecting insulation resistance cannot be well suited for the inverters with multi-inputs. When it is required to measure insulation impedance of photovoltaic (PV) inverters with multi-inputs, a plurality of resistors and switches need to be added. With increase of the number of inputs, the detection circuit and calculation method are becoming increasingly complex. The circuits and methods do not have universality. Alternatively, photovoltaic input is required to be changed by illumination change or artificially, thus obtaining a plurality of equations to solve for the insulation impedance. This detection method is difficult to be controlled automatically, and has poor practicality.